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Are you sure it takes the same time? It takes me an extra hour to fly home from the US, for example (to Europe). And your reasoning is exactly why, if I am not mistaken.
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Flint72May 12 '14 at 12:29

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from Moscow to Toronto it takes 45min longer because of the wind flow but if the speed of the airplane is constant and add the speed of earth rotation, it should take much longer. I guess 13 hours
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SamotnyPocitacMay 12 '14 at 12:32

2 Answers
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Your issue is about moving within a moving referential. To understand it well, let us first consider a Galilean referential: assume you live on a flat infinite plane, which is travelling at a constant speed along a horizontal direction. Does it take you more energy to move along with the movement of the plane or in the other way? No, just as walking to the front or rear of a train going at constant speed. It would if you had some contact with the exterior of the train, e.g. the air.

Now your referential at the surface of Earth is not in translation but in rotation, and that's the origin of Coriolis force, but that is only a correction to the movement in the referential, which works the same as above.

The reason flights take a different amount of time, depending on the direction is prevailing winds, not the earths rotation. This is because the atmosphere rotates with the earth, and the plane has a constant airspeed traveling both ways. However due to the coriolis effect the prevailing winds have a constant eastwards or westwards direction (as explained in this wikipedia article), making the ground speed (airspeed + wind speed) different in both directions.

The effect the earth's daily rotation is on the weight of the airplane due to the centrifugal force (which exists in our frame of reference). This effect is very small and doesn't impact the speed of flight

Ok, back to Toronto-Moscow. As you can see in this map the flight path goes northwards over greenland and closer then normally to the north pole.
Image source

This means that the prevailing winds blow more perpendicularly (east or west) to the planes movements, thus having a smaller impact on the flight duration.

To test this theory I looked up flights between Moscow and Dubai, as they are almost perfectly north/south of each other. And the flight time difference is only 10 mins! Showing thats flights going north or south have a lower difference then those going east/west